Urban atmospheric particle size distribution in Santiago, Chile

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Highlights

  • A one-year record of particle size distribution ranging from 0.28 to 10 μm is presented.

  • The accumulation and coarse modes were identified, with a transition diameter of 1 μm.

  • The accumulation mode contributed with more than 99 % of the total particle number concentration.

  • The contribution of the accumulation mode increased with higher RH and lower T.

Abstract

A monitoring campaign of the atmospheric particulate matter (PM) size distribution (between 0.25 and 10 μm in diameter (Dp)) in an urban area with high levels of air pollution between June 2018 and May, 2019 is presented. The relative contribution of 24 size fractions to the total number and mass concentration of PM was analyzed using an aerosol spectrometer. Local meteorological parameters and their effect on the PM concentrations were also evaluated. The size-fractionated particle mass concentrations showed the accumulation (Dp < 1 μm) and coarse (1 μm < Dp < 10 μm) modes. The highest contribution of the accumulation mode was observed during autumn and winter (reaching 99.7 % and 35.2 % of the total number and mass concentrations, respectively). High relative humidity and low temperatures were strongly correlated with high concentrations for the smaller PM fractions, which can be connected to the increase of residential emissions of PM derived from wood burning sources in winter months. The larger PM fractions showed higher concentrations during the spring and summer months, potentially because of dust resuspension due to the high vehicular traffic in the vicinity. High PM concentrations of the larger fractions were favored by the lack of precipitation events and stronger winds during this time of the year. The results showed the importance of the PM1 fraction to improve the source apportionment studies in urban areas and provide information about the potential health effects associated to high PM concentration events.

Introduction

The deterioration of urban air quality is a global trend and has been a concern for local authorities and researchers, motivating the implementation of monitoring programs and stringent regulations for vehicle and industrial emissions. Improved combustion technologies, cleaner energy sources, cleaner mass transportation systems, better house-heating systems, and the regular cleaning of streets are among the policies implemented by local authorities to cope with this issue. However, the concentrations of some atmospheric pollutants are still on the rise in some urban centers around the world, which can be related to an increase in the demand for energy and resources for an expanding urban population (Chan and Yao, 2008; Fenger, 1999; Gurjar et al., 2016). High concentrations of breathable atmospheric particulate matter (PM) are registered every year in large urban areas such as Beijing, Guangzhou, Seoul, Milan, Athens, Mexico City, Lima, Bogotá, and Santiago (Gouveia and Junger, 2018; Grivas et al., 2008; Kan et al., 2012; Kim et al., 2006; Ozgen et al., 2016; Vargas et al., 2012). These high levels of PM concentrations have been associated with several effects on human health including respiratory and cardiovascular diseases, reduced longevity, and increases in cardiopulmonary mortality rates (Dockery and Pope, 1994; Pope and Dockery, 2006; Russell and Brunekreef, 2009; Schikowski et al., 2007). Additionally, PM can also have effects on the global climate, affecting the radiative balance of the atmosphere and acting as cloud or ice condensation nuclei affecting the process of cloud formation, their properties, and lifetime (Andreae et al., 2005; Heintzenberg, 2012; Kim et al., 2006; Lohmann and Feichter, 2005; Rosenfeld et al., 2008).

Atmospheric PM can have different sizes, morphology, chemical composition, and hygroscopic properties, according to its emission sources and the potential transformation reactions suffered once it is emitted. However, size is what usually determines its ability to penetrate the human respiratory system: PM with aerodynamic diameter (Dp) below 5 μm deposits mostly in the upper respiratory system, while PM with Dp < 2.5 μm can reach the lower portions of the lungs and the alveoli (Dockery and Pope, 1994). Many health effects have also been attributed to smaller PM size fractions, such as ultrafine PM (Dp < 0.1 μm), which have shown stronger correlations to the total number of particles rather that their mass concentration (Klejnowski et al., 2013; Oberdorster et al., 1995; Penttinen et al., 2001; Peters et al., 1997).

PM samples collected in urban environments usually include particles from local primary sources, other produced in secondary atmospheric processes and some transported from nearby sources. Thus, the characteristics of urban PM are greatly affected by local emission sources and vary according to local geographical and meteorological conditions (Buzorius et al., 1999; Dall'Osto et al., 2012; Hussein et al., 2006; Ketzel et al., 2003; Wegner et al., 2012; Titos et al., 2014). Vehicle traffic is considered one of the greatest contributors to urban PM, including PM2.5 (Dp < 2.5 μm), PM10 (Dp < 10 μm), ultrafine PM in the nucleation mode (Dp < 0.01 μm) and in the Aitken mode (Dp < 0.1 μm) with an average size distribution ranging from 0.02 to 0.03 μm (Hei, 2010; Wahlin et al., 2001; Watson et al., 2006).

The Chilean national air quality standards (NAQS) and the guidelines from the World Health Organization (WHO) for atmospheric PM are systematically exceeded in the Santiago Metropolitan Area (SMA) and other cities in Chile (Molina et al., 2017; Toro A et al., 2014). These high concentration episodes are closely associated with local weather conditions (i.e., the presence of thermal inversions, shallow mixed layer, low wind speed, and high relative humidity) (Toro A et al., 2019), but they also depend on the local sources of various PM sizes. It is known that vehicle traffic accounts for 37 %–41 % of PM2.5 in the SMA, according to the latest emissions inventories, followed by residential heating (35 %), industrial sources (11 %) and ongoing construction projects (9 %) (Barraza et al., 2017; USACH, 2014). However, very few studies have focused on smaller PM sizes or on the analysis of the total number of particles (most of the studies in Chile have focused on the analysis of the mass concentrations of PM10 and PM2.5) (Manzano et al., 2021). The only available information shows that PM with Dp < 0.174 μm is associated with vehicular emissions, while PM with Dp > 0.175 μm is associated with wood burning and other combustion sources after one and two weeks of sampling at urban and rural sites, respectively (Gramsch et al., 2014b).

The objective of this study was to explore the urban atmospheric particle size distribution in the SMA, Chile from June 2018 to May, 2019 using an aerosol spectrometer. The effects of local meteorological variables and local sources in the number and concentration of different PM size fractions was explored.

Section snippets

Study area

The SMA (33.5° S, 70.6° W, average elevation of 500 m above sea level, approximate area of 15,500 km2) is the largest urban area in Chile and accounts for 40 % (7.1 million inhabitants) of the country's total population (INE, 2017). The annual average temperature is 14 °C, and average relative humidity is 64 %. Wind speed is generally low (average speed of 2.2 m s−1), and valley-mountain breezes are frequent (Toro A et al., 2014). The sampling site was located inside the University of Chile

Particle size distribution

Fig. 1 shows the size distribution of the particle number and mass concentrations of PM registered between June 2018 and May, 2019, divided into seasons and time of the day. Due to their environmental and public health relevance, and to simplify the analysis, only PM sizes with Dp < 10 μm are shown, which correspond to the first 24 size fractions originally registered by the spectrometer (total analysis range: 0.25 μm–32 μm).

The PM1 fraction (Dp < 1 μm) showed larger particle number

Conclusions

The analysis of the size distribution of breathable atmospheric PM (with size ranging from 0.25 to 10 μm), sampled at a commercial/residential area of the SMA throughout a year, allowed us to identify the PM accumulation and coarse modes which showed comparable concentrations below 100 μg m−3. The accumulation mode showed higher concentration during the cold months of the year (autumn and winter) due to the increased residential emissions derived from wood burning home heating systems, and

Credit author statement

Luis Felipe Sánchez P.: Methodology, Data curation, Formal analysis, Validation, Writing – original draft, Writing – review & editing, Carlos A. Manzano: Writing – original draft, Writing – review & editing, Manuel A. Leiva G.: Writing – review & editing, Visualization, Mauricio Canales A.: Writing – review & editing, Richard Toro A.: Conceptualization, Investigation, Methodology, Formal analysis, Visualization, Supervision, Writing – original draft, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Richard Toro A., Carlos A. Manzano and Manuel Leiva G. acknowledges the financial support by the Chilean National Fund for Scientific and Technological Development (FONDECYT) Projects Grants No. 11150931, 11180151, 1200674 and by the Chilean National Fund for Scientific and Technological Equipment Project Grant No. EQM190045.

References (57)

  • T. Hussein et al.

    Meteorological dependence of size-fractionated number concentrations of urban aerosol particles

    Atmos. Environ.

    (2006)
  • H. Kan et al.

    Ambient air pollution, climate change, and population health in China

    Environ. Int.

    (2012)
  • M. Ketzel et al.

    Particle and trace gas emission factors under urban driving conditions in Copenhagen based on street and roof-level observations

    Atmos. Environ.

    (2003)
  • Y.J. Kim et al.

    Fine particulate matter characteristics and its impact on visibility impairment at two urban sites in Korea: Seoul and Incheon

    Atmos. Environ.

    (2006)
  • G. Titos et al.

    Identification of fine (PM1) and coarse (PM10) sources of particulate matter in an urban environment

    Atmos. Environ.

    (2014)
  • R. Toro A et al.

    Exploring atmospheric stagnation during a severe particulate matter air pollution episode over complex terrain in Santiago, Chile

    Environ. Pollut.

    (2019)
  • R. Toro A et al.

    Inhaled and inspired particulates in Metropolitan Santiago Chile exceed air quality standards

    Build. Environ.

    (2014)
  • F.A. Vargas et al.

    PM10 characterization and source apportionment at two residential areas in Bogota

    Atmos. Poll. Res.

    (2012)
  • A.M. Villalobos et al.

    Chemical speciation and source apportionment of fine particulate matter in Santiago, Chile, 2013

    Sci. Total Environ.

    (2015)
  • Y. Wang et al.

    Statistical analysis and parameterization of the hygroscopic growth of the sub-micrometer urban background aerosol in Beijing

    Atmos. Environ.

    (2018)
  • T. Wegner et al.

    Properties of aerosol signature size distributions in the urban environment as derived by cluster analysis

    Atmos. Environ.

    (2012)
  • Y. Wu et al.

    Investigation of hygroscopic growth effect on aerosol scattering coefficient at a rural site in the southern North China Plain

    Sci. Total Environ.

    (2017)
  • D. Zhao et al.

    The formation mechanism of air pollution episodes in Beijing city: insights into the measured feedback between aerosol radiative forcing and the atmospheric boundary layer stability

    Sci. Total Environ.

    (2019)
  • B. Zhou et al.

    Daily variations of size-segregated ambient particulate matter in Beijing

    Environ. Pollut.

    (2015)
  • M.O. Andreae et al.

    Strong present-day aerosol cooling implies a hot future

    Nature

    (2005)
  • F. Barraza et al.

    Temporal evolution of main ambient PM2. 5 sources in Santiago, Chile, from 1998 to 2012

    Atmos. Chem. Phys.

    (2017)
  • M. Dall'Osto et al.

    Urban aerosol size distributions over the Mediterranean city of Barcelona, NE Spain

    Atmos. Chem. Phys.

    (2012)
  • D.W. Dockery et al.

    Acute respiratory effects of particulate air pollution

    Annu. Rev. Publ. Health

    (1994)
  • Cited by (2)

    Peer review under responsibility of Turkish National Committee for Air Pollution Research and Control.

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